Same issue here with Catalina 10.15.1 Beta (19B77a). I have yet not managed to have it working but I slightly improved the situation:
I went to System Preferences > Security & Privacy > General and allowed STM32CubeIDE.app:
IDE was able to launch but it takes a very long time with "Checking for Updated Files ..." modal. I cannot Cancel or Close this modal window.
As well, there is an issue with "st-stlink-server.1.2.0-3.pkg": This package is incompatible with this version of macOS.
Installation log:
11:51:28+03 Installer[3042]: ST Link Server Installation Log
11:51:28+03 Installer[3042]: Opened from: /Volumes/STM32CubeIDE/st-stlink-server.1.2.0-3.pkg
11:51:28+03 Installer[3042]: No localized entry for ../common/license
11:51:28+03 Installer[3042]: Package Authoring Error: <background_scaling> has an unsupported MIME type: X-NSObject/NSNumber
11:51:28+03 Installer[3042]: Package Authoring Error: <background_alignment> has an unsupported MIME type: X-NSObject/NSNumber
11:51:28+03 Installer[3042]: Package Authoring Error: <layout-direction> has an unsupported MIME type: X-NSObject/NSNumber
11:51:28+03 Installer[3042]: Failed to load specified background image
11:51:28+03 Installer[3042]: Product archive /Volumes/STM32CubeIDE/st-stlink-server.1.2.0-3.pkg trustLevel=100
11:51:28+03 Installer[3042]: External component packages (1) trustLevel=100 (trust evaluation failed: Error Domain=PKInstallErrorDomain Code=101 "The package “st-stlink-server.1.2.0-3.pkg�? is not signed." UserInfo={NSURL=#tmp.pkg -- file:///Volumes/STM32CubeIDE/st-stlink-server.1.2.0-3.pkg#Distribution, PKInstallPackageIdentifier=com.st.pkg.st-stlink-server, NSLocalizedDescription=The package “st-stlink-server.1.2.0-3.pkg�? is not signed.})
11:51:28+03 Installer[3042]: Could not load resource readme: (null)
11:51:28+03 Installer[3042]: No localized entry for ../common/license
11:51:28+03 Installer[3042]: Could not load resource license: (null)
11:51:57+03 Installer[3042]: ================================================================================
11:51:57+03 Installer[3042]: User picked Standard Install
11:51:57+03 Installer[3042]: Choices selected for installation:
11:51:57+03 Installer[3042]: Install: "ST Link Server"
11:51:57+03 Installer[3042]: Install: "Install"
11:51:57+03 Installer[3042]: st-stlink-server.1.2.0-3.pkg#tmp.pkg : com.st.pkg.st-stlink-server : 1.2.0-3
11:51:57+03 Installer[3042]: ================================================================================
11:51:57+03 Installer[3042]: It took 0.00 seconds to summarize the package selections.
11:51:57+03 Installer[3042]: -[IFDInstallController(Private) _buildInstallPlanReturningError:]: location = file://localhost
11:51:57+03 Installer[3042]: -[IFDInstallController(Private) _buildInstallPlanReturningError:]: file://localhost/Volumes/STM32CubeIDE/st-stlink-server.1.2.0-3.pkg#tmp.pkg
11:51:57+03 Installer[3042]: Set authorization level to root for session
11:52:08+03 Installer[3042]: Administrator authorization granted.
11:52:08+03 Installer[3042]: Will use PK session
11:52:08+03 Installer[3042]: Using authorization level of root for IFPKInstallElement
11:52:08+03 Installer[3042]: Package Authoring Error: Package contains system volume install location content. Installation cannot proceed since installing to the system volume is not possible.
11:52:08+03 Installer[3042]: Package Authoring Error: Package contains system volume install location content, and installation will fail: Error Domain=IFInstallErrorDomain Code=-6000 "This package is incompatible with this version of macOS." UserInfo={NSLocalizedRecoveryOptions=(
Quit
), IFReadOnlyPathsKey={(
"/delivery"
)}, NSLocalizedRecoverySuggestion=The package is trying to install content to the system volume. Contact the software manufacturer for assistance., NSLocalizedDescription=This package is incompatible with this version of macOS.}
11:52:14+03 Installer[3042]: Client requested cancelation of install following warning.
11:52:14+03 Installer[3042]: Halting PK session due to client response to warning This package is incompatible with this version of macOS.
11:52:14+03 Installer[3042]: Install failed: The Installer could not install the software because there was no software found to install.
